1. Field of the Invention
The present invention relates to removing gaseous sulfur compounds from gaseous streams, particularly the removal of SO.sub.2 and H.sub.2 S from combustion and industrial process effluents, by using a regenerable catalyst/sorber.
2. Related Art
As one result of concern with air pollution, environmental regulators have severely reduced and are continuing to reduce allowable emissions of sulfur oxides and hydrogen sulfide. As a result, a variety of technologies have been developed and are continuing to be developed for use in flue gas desulfurization (FGD).
FGD techniques can generally be classified as wet and dry scrubbing. Dry scrubbing contacts the effluent with a solid material which chemically reacts with the sulfur component and forms a compound. The system can be a fixed bed such as zinc oxide pellets that are used to react with H.sub.2 S to form zinc sulfide. The zinc sulfide pellets must be removed and replaced after saturation. The dry scrubber can also be in powder or particulate injected into the stream followed by a baghouse or electrostatic filtration to remove the reacted product. An example of powder would be limestone, which would react after injection into the exhaust stream to form calcium sulfate and/or calcium sulfite hemihydrate sludge. The material is typically delivered as a wet slurry, which dries in the exhaust and reacts with the sulfur oxides. This material is then removed and typically disposed of in a landfill. There are also regenerable dry scrubber materials such as copper oxide on aluminum oxide pellets or spheres. The regenerable copper systems must be heated to and or reduced at high temperatures. This technique requires that the sorption temperature be less than the regeneration temperature.
Wet scrubbing techniques use wet slurries or amine solutions and require that the exhaust temperature be reduced to below the boiling point of the solutions to be used. These techniques give rise to losses by evaporation and entrainment and produce products which are contaminated and unusable and must be disposed of /or purified before reuse.
The present invention introduces a new technology for the removal of H.sub.2 S, SO.sub.2 and oxidation of CO. This technology utilizes a catalytic oxidative sorption process for the removal of the sulfur component where the sulfur component is first oxidized and preconcentrated and then released in a concentrated stream of much smaller volume which is delivered to processes for recovery as sulfur, sulfur dioxide, or sulfuric acid. This technology has tremendous advantages over the scrubbing techniques. It is an advantage that the present process operates in the exhaust stream with oxidative capture mode and reductive regeneration occurring at the same temperature. It is a further advantage that it is a dry process, which is selective for sulfur components and will produce sulfur oxide off gases with high concentration and purity. It is a feature of the present invention that it reduces the volume of sulfur containing gases thereby reducing the costs for further processing. It is a further feature that the process also operates over a wide range of temperatures (200.degree. F. to 800.degree. F.). It is another advantage of the process of the present invention that it has high capture efficiencies of over 99.75% and also has very low pressure drop.